Quantum noise thermometry for bosonic Josephson junctions in the mean field regime

摘要

Bosonic Josephson junctions can be realized by confining ultracold gases ofbosons in multi-well traps, and studied theoretically with the $M$-siteBose-Hubbard model. We show that canonical equilibrium states of the $M$-siteBose-Hubbard model may be approximated by mixtures of coherent states, providedthe number of atoms is large and the total energy is comparable to $k_BT$.Using this approximation, we study thermal fluctuations in bosonic Josephsonjunctions in the mean field regime. Statistical estimates of the fluctuationsof relative phase and number, obtained by averaging over many replicates of anexperiment, can be used to estimate the temperature and the tunnelingparameter, or to test whether the experimental procedure is effectivelysampling from a canonical thermal equilibrium ensemble.